The present invention relates to a device and a method for evaluating the effectiveness of can coatings intended for use in a primary alkaline battery cell. In the method, it is possible to observe the electrical resistance changes that would occur at the can to cathode interface in a primary alkaline cell. A low can to cathode resistance is key to high rate performance in alkaline cells. The device and method negate the need to produce an actual primary alkaline cell to evaluate a prospective can coating. Candidate can coatings must also be tested for their ability to withstand xe2x80x9cagingxe2x80x9d in the battery while in the retail store supply chain for periods of up to two years or longer. The method of the present invention therefore incorporates an accelerated xe2x80x9cagingxe2x80x9d process whereby the device is exposed to an elevated temperature of 160xc2x0 F. for a period of 28 days to simulate storage of 2 years at ambient temperature in the supply chain.
One of the critical variables in designing a high performance alkaline battery cell is the resistance to electrical current flow encountered at the interface between the inside surface of the battery can and the cathode mix contained within the can. More particularly, a coating applied to the inside surface of the metal can which effectively survives the oxidizing power of the cathode mix and the highly alkaline environment of the battery cell will in effect reduce the interfacial resistance and will result in a better battery. Coatings for the inside surface of the alkaline battery can are numerous and are receiving much attention. Metal coatings such as electroplated nickel (Thomas Steel Co. U.S. Pat. No. 2,115,750), electroplated nickel-cobalt (Hille and Muller U.S. Pat. No. 4,910,096) and carbon paint (Matsushita Electric U.S. Pat. No. 5,316,557, Rayovac U.S. Pat. No. 5,447,809 and Toyo Kohan U.S. Pat. No. 5,792,553) have all been shown to improve the high rate performance of an alkaline cell. Various combinations of plating, annealing and carbon painting have been shown to even further improve the performance of the alkaline cell as demonstrated by cell testing.
The capability of evaluating coatings for the interior of alkaline cells has until now, been limited to the alkaline battery manufacturers. In order to evaluate a potential new coating it was necessary in the past to produce an actual alkaline cell and test it under high rate conditions. Sometime these cells are xe2x80x9cagedxe2x80x9d at high temperature to simulate storage in the xe2x80x9csupply chainxe2x80x9d. In either case, the can coating was evaluated for its ability to sustain high discharge currents. It is an unmet desire of the prior art to provide a proper test device and test method for measuring the time dependence of resistance as measured at the interface between the can and the cathode mix without the need for constructing an actual alkaline cell.
This advantage and other advantages of the present invention are provided by a method for manufacturing a device for evaluating the effectiveness of can coatings intended for use in a primary alkaline battery cell. Such a method comprises the steps of: (a) forming a cup and a test disk from a material, with the can coating applied to the interior surface of the cup and to one surface of the disk; (b) forming a lightly compacted disk of a simulated cathode mix in the cup; (c) placing the test disk onto the lightly compacted cathode mix such that the coated side of the metal disk is in electrical contact with the cathode mix disk, an opposite surface of the test disk is not in electrical contact with the cathode mix disk and the test disk is not in direct electrical contact with the cup; (d) compacting the contents of the cup tightly to create intimate electrical contact between the cathode mix and the test disk and the cathode mix and the interior surface of the cup; (e) forming a sealing cap from an electrically nonconductive material atop the test disk and the cathode mix in the cup to maintain the contents of the cup in a compacted state; and (f) providing electrical contact to a portion of the test disk.
Even further advantages of the invention are achieved by a device for evaluating the effectiveness of can coatings intended for use in a primary alkaline battery cell. The devices comprises a cup of a coated material, a disk of the coated material, an amount of simulated cathode mix; and a sealing cap. The coating is applied to an interior surface of the cup, and to at least one surface of the disk, either before or after the cup and disk are formed from a base material. The cathode mix is interposed between the interior surface of the cup and the coated surface of the disk and is compacted into intimate electrical contact with the both the disk and the cup in a manner that the disk is not in direct electrical contact with the cup. The sealing cap is formed from an electrically nonconductive material atop the disk and the compacted cathode mix in the cup to maintain the contents of the cup in a compacted state.